This invention generally relates to turbine technology and, more specifically, to turbine buckets or blades formed with integral tip shrouds.
Tip shrouds located at the tips of turbine buckets or blades dampen vibrations and support the tip areas of the airfoil portions of the buckets. Tip shrouds also form the radially outer boundary of the hot gas flow path through the turbine stage. As such, tip shrouds span from one bucket to another and make contact at their oppositely-facing circumferential edges. Forward and aft edge portions of the tip shroud typically overhang the airfoil and it is these areas that are often exposed to higher temperatures and high bending stresses. These overhung areas can also creep, and even creep to rupture, before the useful service life of the entire bucket is consumed, thus limiting the life of the bucket.
Tip shrouds are often formed integrally with the bucket airfoil and may also support integral seal teeth designed to prevent hot gas leakage around the outer edges of the shrouds. The bucket or airfoil and tip shroud are usually formed by casting, and the tip shroud is typically machined to its final figuration.
The overhung forward and aft edge portions of the tip shrouds are often scalloped, removing overhung material, to reduce mass in these areas but this reduces the tip shroud outer flow path coverage, and thus reduces efficiency. In addition, the material for the bucket is generally selected as the lowest-temperature and lowest-cost alloy that can withstand the stresses and service life requirement for the airfoil portion.
It would therefore be desirable to provide a tip shroud configuration that is less prone to creep and thus more favorable in terms of meeting the predicted service life of the bucket.